Former vice president Joe Biden opened his third campaign for the presidency on Thursday, taking direct aim at President Donald Trump and declaring that "we are in the battle for the soul of this nation."

In a video posted on social media, Biden recounted the deadly clash between white supremacists and counterprotesters at a 2017 gathering in Charlottesville, Virginia, after which Trump said there were "some very fine people on both sides."

"In that moment, I knew the threat to this nation was unlike any I had seen in our lifetime," Biden said, adding: "The core values of this nation - our standing in the world, our very democracy, everything that has made America America - is at stake. That's why today I'm announcing my candidacy for president of the United States."

As he joined a crowded Democratic field in which many candidates have staked out progressive positions on an array of issues, Biden made no mention of policy specifics in the 3 1/2-minute video, which also stood out for how directly he confronted Trump.

Biden, 76, who served for eight years as the second-in-command to the last Democrat to successfully seek the presidency, holds a strong position in early polls, but the trajectory of his campaign is uncertain.

Biden made his announcement hours before a major campaign fundraiser was to take place in Philadelphia. His first campaign event, union-themed, is planned Monday in Pittsburgh, a Democratic city whose suburbs and exurbs are filled with the sort of voters who abandoned the Democratic Party to side with Trump in 2016.

After that, his campaign said, Biden will travel to several early nominating states.

His campaign also announced two dozen senior staff members Thursday afternoon.

Biden, who made his first bid for the White House more than 30 years ago, is scheduled to appear Friday on "The View," in what the ABC program said in a tweet would be his first sit-down interview since announcing his candidacy.

Trump responded to Biden's entrance about two hours after he announced.

"Welcome to the race Sleepy Joe," he wrote on Twitter. "I only hope you have the intelligence, long in doubt, to wage a successful primary campaign. It will be nasty - you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!"

Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign. It will be nasty - you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!

Biden's announcement day also faced a distraction from rare public comments by Anita Hill, the law professor who had accused then-Supreme Court nominee Clarence Thomas of sexual harassment in hearings in 1991 that Biden directed as chairman of the Senate Judiciary Committee.

Biden has long been criticized for the committee's treatment of Hill. In an interview with The New York Times, Hill said she could not support his campaign.

"I cannot be satisfied by simply saying 'I'm sorry for what happened to you,' " she said. A senior campaign aide confirmed Thursday that Biden had talked with Hill; the aide disclosed no other details.

A Democratic force for nearly five decades, Biden built his career as a campaigner on his connection with working-class voters, including white voters he has sometimes called "the ethnic vote" - Midwestern Irish, Italian and Polish Catholics, or South Florida Jews. His campaign style tends toward the populism of Franklin Roosevelt, railing against those with money and power who he claims work against the needs of middle-class Americans.

"They don't understand us middle-class folks," Biden thundered repeatedly from the stump in 2012, when he was campaigning against then-Republican nominee Mitt Romney.

After Trump’s election in 2016, Biden made clear that he believed the cause was a failure by Democrats to connect with working voters.

"You didn't hear a single solitary sentence in the last campaign about that guy working on the assembly line making 60,000 bucks a year and a wife making $32,000 as a hostess in restaurant," he said in a 2017 appearance at the University of Pennsylvania.

At the same time, Biden also is expected to play up - and benefit from - his tenure as vice president to the nation's first black president. In early polling, Biden has been popular among black voters, who make up a dominant Democratic voting bloc in many states. Former president Barack Obama has indicated, however, that he will not make an early endorsement in the race.

In a statement shortly after the release of Biden's video, an Obama spokeswoman praised Biden's tenure as vice president but stopped short of offering the former president's endorsement.

"President Obama has long said that selecting Joe Biden as his running mate in 2008 was one of the best decisions he ever made," said Obama spokeswoman Katie Hill. "He relied on the vice president's knowledge, insight and judgment throughout both campaigns and the entire presidency. The two forged a special bond over the last 10 years and remain close today."

Speaking briefly to reporters Thursday at the Amtrak station in Wilmington, Delaware, Biden said he had asked Obama not to make an endorsement in the Democratic nominating contest.

"Whoever wins the nomination should win it on their own merits," Biden said.

Asked why he's the best choice for Democrats, Biden said, "That will be for the Democrats to decide."

He later made an appearance at a Wilmington restaurant where he ordered a pepperoni pizza to go and mingled with patrons. On the way out, he was asked by a reporter if he had a message for the world.

"America's coming back like we used to be - ethical, straight, telling the truth . . . supporting our allies, all those good things," Biden said.

As he finalized his run, Biden was buffeted by scrutiny for a wide range of positions that, in some cases, were in line with Democratic orthodoxy long ago but are now out of step - a circumstance that may presage what awaits him in the campaign.

Those include support for anti-busing legislation in the 1970s, his role handling the testimony of Anita Hill during Senate hearings to confirm Clarence Thomas as a Supreme Court justice, and his arm-twisting on behalf of a crime bill in the 1990s. He has attempted to address some of those issues in recent weeks but has often stumbled.

"To this day, I regret I couldn't come up with a way to get her the kind of hearing she deserved," Biden said last month of the hearings on Thomas's nomination, which he directed as chairman of the Senate Judiciary Committee.

He has also come under criticism in recent weeks for his hands-on style. Several women have said made he them feel uncomfortable with hugs, pressing his forehead against theirs, or, in one case, smelling a Nevada politician's hair.

Biden posted a video saying that "social norms are changing" and that he would be "much more mindful." Two days later, however, he twice joked about the complaints during a speech to union workers.

Biden and his team worked to try to engineer a show of force at his entrance, both from organized groups loyal to him and from donors. Shortly after his announcement, he received several endorsements, including from Sen. Christopher A. Coons (D-Del.), who succeeded Biden after he left the Senate to become vice president.

In a statement, Coons said Biden was "better prepared than anyone to lead America on the world stage at a time when our commitments to our allies and our values are being questioned like never before."

The Republican National Committee also quickly sought to define Biden in a far less flattering light, calling him a "gaffe machine" and noting that Obama was not offering his endorsement.

"Joe Biden has been running for president and losing since the '80s," said RNC spokesman Michael Ahrens. "2020 won't be any different. Biden's fingerprints are all over foreign policy blunders and the weakest economic recovery since World War II. We don't need eight more years of Biden."

For months, a tight group of current and former advisers has been knitting together a campaign plan to prepare for a run, talking with him as he has vacillated on his desire to throw his hat in the ring. They include Steve Ricchetti, a former lobbyist who served as his last chief of staff in the White House; former senator Ted Kaufman, D-Del., a longtime friend whom he helped appoint to his vacant Senate seat after the 2008 election; and Mike Donilon, a longtime aide.

A broader network of friends and former aides has signaled hope for months that Biden would enter the race so they can join his campaign, an advantage his aides hope will allow him to quickly pull together a large organization. An underwhelming fundraiser in his first two campaigns for president, he is likely to be aided this time by deep-pocketed donors he got to know during the Obama years.

"We need to get more pragmatic and understand that Joe Biden is the only real chance to win in 2020," said Dick Harpootlian, former chairman of the South Carolina Democratic Party. "My concern is our nominee has to be able to carry Pennsylvania, Ohio and Michigan - and I don't see that in any of these other folks."

Biden considered a late entry into the 2016 Democratic nomination fight, as a challenger to former secretary of state Hillary Clinton, but decided against it as he mourned the death of his eldest son, Beau, from brain cancer at age 46. He later wrote a book explaining his decision as a personal one based on his emotional turmoil after his son's death.

Biden's earlier presidential races were disappointments. His first run, in 1988, was derailed by scandal when it was revealed that he had lifted parts of his stump speech from British Labour Party leader Neil Kinnock, among others. Two decades later, Biden cast himself in his second presidential run as the most experienced Democratic candidate in the field, especially on matters of national security.

"Ladies and gentlemen, I have forgotten more about how to fight terror than Rudy Giuliani will ever learn," he said in one of his last rallies before the Iowa caucuses, referring to the mayor of New York at the time of the Sept. 11, 2001, terrorist attacks. "The test for this presidency is clear. It is crystal clear: Who can take these guys on, and who is ready from day one?"

Biden won less than 1 percent of the delegates in the 2008 Iowa caucuses, however, and dropped out of the race shortly afterward. Seven months later, Obama selected him as his running mate, a credit both to Biden's experience as an inside player in Washington and to his perceived appeal among Midwestern voters.

In the White House, he was a constant presence in decision meetings, weighing in with Obama on a broad range of issues. He was also given special briefs, including the implementation of the 2009 stimulus bill, a failed effort to change gun laws after the 2012 shooting at Sandy Hook Elementary School and as a lead White House negotiator with congressional Republicans during budgetary standoffs.

Obama, who has remained a close friend and frequent booster of Biden, has spent the years since leaving the White House focused on developing "the next generation" of Democratic talent. Advisers say that has not been intended as a signal for Biden not to run, though Biden has written that he believed Obama tried to indirectly discourage him from entering the 2016 election during their private conversations.

At one point, the vice president met with an Obama pollster who argued, Biden wrote, that "I had no real path to the nomination" in a contest against Clinton.

First elected to the U.S. Senate by Delaware voters in 1972, at the age of 29, Biden went on to six reelections, serving as the chairman of the Judiciary Committee during contentious confirmation battles over Supreme Court nominees Thomas and Robert H. Bork , and as chairman of the Foreign Relations Committee at the time of the 2001 terrorist attacks on the World Trade Center and the Pentagon.

Like Clinton, he voted as a senator in 2002 to authorize the use of force in Iraq, which cleared the way for a war launched by President George W. Bush. Biden later said he regretted the vote. During the 2012 campaign, Biden praised Obama for overlooking his objections to approving a secret raid that led to the killing of Osama bin Laden, the mastermind of the 2001 attacks. He later said he privately encouraged Obama to move forward with the raid in a separate conversation.

In recent months, he has been less aggressive than other presidential hopefuls in recruiting staffers, building an email list or reaching out for support in the early-voting states of Iowa, New Hampshire and South Carolina.

He did travel the country in the run-up to the 2018 midterms, campaigning for Democratic candidates with a message that is likely to pop up in his presidential campaign.

“We have to make clear that Democrats, Democrats choose hope over fear. Democrats choose unity over division, and most importantly, we choose truth over lies,” Biden said. “It’s time to get up. Remember who in the hell we are. This is America.”